What OTHER OS' are there????
Lots. It wouldn't make sense to break down linux by distribution though, there are just so many. But, there is also FreeBSD, OpenBSD, NetBSD, Minix, Solaris, Plan 9, Inferno, GNU/HURD, OpenDarwin, and several more Unix-likes. Then there are the non-Unix-likes...
But it wouldn't make sense to include any of these beyond maybe the BSDs (all as one option) and then maybe Plan9 and Solaris. They are just too unpopular.